Development of the GL32J-40P Cylindrical Grinding Machine

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Annice Cummings
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1 TECHNICAL REPORT Development of the GL32J-40P Cylindrical Grinding Machine K. OKADA The GL32J-40P is a cylindrical grinding machine used to grind cylindrical sections of powertrain components such as gears and transmission shafts. It was developed with the aim of being a simple, slim, and low-cost machine that is space-efficient, robust, and highly reliable. Both the JTEKT GC50 and FANUC models are available as standard CNC options, from which customers may choose depending on which enables easier operation. Both the in-house CNC model GC50 and the FANUC CNC are available on this machine and can be selected depending on which model eases operation for that individual customer. Key Words: cylindrical grinding machine, transmission shaft, wheelhead traverse, wheel spindle bearing, center trough, slidebase-mounted auto-sizer 1. Introduction The remarkable economic development in recent years in Asian countries, spearheaded by China and India, has caused a shift in traffic from bicycles to motorcycles and further to automobiles. In the automotive industry, where competition has been growing ever more intensive, the biggest challenge we face is the establishment of flexible production lines which can promptly deal with changes in the market. As such, we are required to make production lines a mixed flow of multiple products and we must use multi-purpose equipment that facilitates line changes in order to increase up-time ratio. Furthermore, in the midst of fierce competition, more compact equipment is favored because it is important for cost saving to improve production efficiency per unit floor area. In processing lines for transmission parts, the workpieces are often hand carried by the operator from one machine to another. Therefore, the introduction of thinner, more compact machines which reduce the operator's required traveling distance will greatly contribute to the improvement of productivity (e.g. the baseline machine GL4E: 3 200mm vs. the developed GL32J: 1 800mm). In addition, since the transmission part processing market is very competitive with many machine builders participating, such low cost machines that have machine spaces best fitted for the workpieces are desired. Presented here is a cylindrical grinding machine for the processing of transmission shafts developed as "optimum equipment best fit for workpieces" with simplicity, slimness, compactness and low cost to replace the more versatile baseline machines being its main design goals (Fig. 1). Fig. 1 GL32J-40P CBN cylindrical grinding machine 2. Development Targets The following subsections concern the targets at which development was aimed High Speed/High Accuracy Slidebase-mounted auto-sizer Improvement of indirect auto-sizing accuracy Chatterless, high stiffness, 3-point support bed Slide feed accuracy 2. 2 Series Encompassing Wide Specification Range Workpiece overall length: from 100mm (for processing gears) to 400/630mm (for processing transmission shafts) Straight slide type for cylindrical grinding and angular slide type for cylindrical/face compound grinding Regular grinding wheel specification and CBN wheel specification 101

CNC control system: GC50 and FANUC Diverse wheel surface speeds Coolant gutter 2. 3 Small/Simple/Flexible Floor space saving Simple, flexible tooling 2.

5 Maintenance/ SV *1 -Less Wheel spindle with rolling bearing SV-less Coolant flow Fig. 2 Coolant center collection (center trough) 3.

2 CNC control system: GC50 and FANUC Diverse wheel surface speeds Coolant gutter 2. 3 Small/Simple/Flexible Floor space saving Simple, flexible tooling 2. 4 High Reliability Visualization of abnormalities Isolation of electrical parts from the coolant splashing areas 2. 5 Maintenance/ SV *1 -Less Wheel spindle with rolling bearing SV-less Coolant flow Fig. 2 Coolant center collection (center trough) 3. Features of Developed Machine The following subsections describe the features of the developed machines relative to the development targets High Speed/High Accuracy Slidebase-mounted Auto-sizer If diverse workpieces are to be processed in one machine with direct auto-sizing, or if multi-stage processing is required with stringent accuracy, it is necessary to have the auto-sizer travel in parallel with the traverse feed of the wheel. In the developed machine, this behavior is attained by mounting the auto-sizer on the traversing base of the wheelhead Improvement of Indirect Auto-Sizing Accuracy Since the baseline machine has such a bed design that includes a coolant outlet only on one side, stiffness of the bed on the coolant outlet side is lower than the other side. This lateral variation of the bed stiffness makes the machine more susceptible to the influence of grinding heat. In the developed machine, therefore, a central trough design is adopted for the bed to accommodate the coolant gutter directly under the grinding operation so that the coolant embracing grinding heat can be let out quickly and the laterally symmetrical bed design may also help to improve the indirect auto-sizing accuracy (Fig. 2) Chatterless, High Stiffness, 3-Point Support Bed If the number of bed supporting jacks is large, the bed supporting stiffness is liable to shift due to geostatic changes in the ground on which the machine is installed, whereas the 3-point supported bed is less vulnerable to such effects. All the developed machines are designed by 3D-CAD to create a high stiffness 3-point support bed based on a structural analysis by 3D-CAD (Fig. 3). Fig. 3 3-point support bed Slide Feed Accuracy The developed machine incorporates a roller slide in place of the conventional V-plane slide so that the binding force is increased, thereby enhancing the feed stiffness. Thus, the tilting of the grinding wheel caused when reversing the direction of the traverse feed can be minimized Series of Wide Specification Range Workpiece Overall Length 100mm (for gear processing) and 400/630mm (for transmission shaft processing) In order to offer the customer with the smallest possible machine suitable for the overall length of workpieces, we have developed a machine with a 100mm processing range (for gear processing) as well as machines of a 400/630mm range (for transmission shaft processing) Straight Slide Type and Angular Slide Type The baseline wheelhead traversing type machine is limited to only the straight in-feed slide type. For the developed machines, the angular in-feed slide is also made available. This has enabled us to offer a wheelhead traverse type machine that takes up the minimal amount of floor space for workpieces requiring simultaneous cylindrical and face grinding. 102

3 Regular & CBN Grinding Wheel Specifications The wheelhead traverse machines have conventionally been available with CBN specifications only. However, there are many transmission shafts that require wide grinding or multi-stepped plunge grinding which are difficult to perform with the CBN wheel. To cope with such workpieces, wheelhead traverse machines for regular wheel specifications have also been developed CNC Control System:GC50 or FANUC For each developed machine, the customer can choose either of the two control systems: GC50, which is JTEKT's unique system that emphasizes the visualization of maintenance conditions, or FANUC, a system commonly used in the industry. This allows customers who have used FANUC CNC to select standard models that they are accustomed to Fig. 4 Machine layout Diversified Wheel Surface Speeds The developed machine is available with wheel surface speeds of 45 m/s or 60 m/s for regular wheel specifications, and 45, 60, 80, or 120 m/s for CBN wheel specifications. As such, an optimal wheel surface speed can be selected depending on the material of the workpiece, the cycle time, and the tool cost. Table 1 GL32J series Simple, Flexible Tooling With a center height of 1 000mm and a depth of work center of 400mm, the developed machine has done away with a foot step. This improved operator access has enabled manual material handling without a conventional ejector (simplified unloading mechanism) (Fig. 5). In addition, the rams of the workhead on both sides are equipped with a longitudinal adjustment function via an NC axis so that various workpieces with different overall lengths can be processed. As it uses a friction drive on both centers, flexible processing of varying workpieces has been made possible without using conventional hardware (Fig. 6) Small/Simple/Flexible Floor Space Saving The adoption of the wheelhead traverse and the reduction in size of the surrounding devices combine to reduce the total required floor space by 40% compared to the baseline machine (GL4E-32). Thus, the smallest machine width in the class has been attained (Fig. 4). Fig. 5 Free of foot step 103

3. 5. 2 SV-less When the baseline machine is relocated, machine parts such as the cover are required to be disassembled and restored for the installation of necessary parts as well as to tune the

4 SV-less When the baseline machine is relocated, machine parts such as the cover are required to be disassembled and restored for the installation of necessary parts as well as to tune the machine. The developed machine is so constructed that such tuning work is not required. 4. Machine Specifications Connector for proximity switch/pressure switch Truing device motor Spindle driving motor Fig. 6 Tooling 3. 4 High Reliability Abnormality Visualization The developed machine incorporates a local cover to prevent the coolant from splashing into areas other than the tooling area. This was done so that those areas where coolant is not splashed may be observed from outside the cover. Also, this machine adopts a roller slide so as to make the slide and the ball screw clearly visible. Thus, the feeding unit can be observed from outside the cover which enables the early detection of any abnormalities Isolation of Electrical Devices from Coolant Splashing Areas Through the use of a local cover, it is possible to locate the electrical devices on the wheelhead and the workhead (including all motors) in open areas so that overall reliability can be improved (Fig. 7). Fig. 7 Isolation of electrical instruments from coolant area 3. 5 Maintenance/SV-less Rolling Bearing on Wheel Spindle In collaboration with the Bearing/Driveline Business Headquarters, a rolling bearing is incorporated on the wheel spindle in place of the conventional fluid bearing. This does away with ancillary devices such as the pump unit and chiller which eliminate a number of maintenance and check items. The specifications of the developed machines are summarized in Table 2. Table 2 Specifications of machines u u u u u u 104

5 5. Conclusion We have developed a cylindrical grinding machine significantly different from the conventional machines on the market today by incorporating a wheel spindle with rolling bearings, a roller slide and a central collection of coolant. The development is extended to a wide series of machines which adapts machine space and cost as suited to the workpieces that need to be processed. We hope to continue the development of machines that would preemptively meet the customer's future needs. *1 SV stands for "supervisor." K. OKADA * * Product Development Department, Machine Tools & Mechatronics Division Headquarters 105

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